This invention relates to a two axes control system for controlling a tanker aircraft boom during refueling operations.
While the primary use of the present invention is in the field of in-flight refueling of aircraft and it is generally described in that environment, the invention is also useful for related purposes. For example, this invention is useful wherever a single operating lever coordinates two axes of control, e.g. construction equipment or aircraft flight controls.
Currently, various systems are used for the in-flight refueling of receiver aircraft by another tanker aircraft. One system employs a drogue/probe device, where the receiver aircraft includes a probe which is literally flown into a drogue unit. The drogue is a funnel shaped receptacle attached to a long hose suspended from the tanker aircraft. While this system has enjoyed some success, it requires the various receiving aircraft to be capable of precise control, and carry a fixed or telescoping boom to support the probe. Since the refueling hose must be extended and retracted from the tanker, as on a reel, the hose must be small in diameter, severely restricting the rate of refueling.
Another system currently in vogue comprises a boom which extends downwardly and rearwardly from the tanker aircraft. The receiver aircraft connects to a nozzle located at the end of the boom. This invention is directed to improving the control of aerial boom type in-flight refueling systems.
One of the major problems characteristic of current aerial boom type in-flight refueling systems is boom whip upon disconnect. The magnitude of the boom excursion upon disconnect is a function of the stress in the boom created by failure of the boom to follow differential movement between the tanker and receiver aircraft. The existing systems require the boom operator to manually follow receiver aircraft excursions to alleviate boom stress. An object of this invention is to employ an automatic load alleviation system wherein boom forces and position are sensed and the resultant signals fed back and translated into boom control by automatically backdriving the stick to alleviate the boom forces. The automatic load alleviation mode of operation, however, allows for manual override of the system by the operator at any time.
Another object of this invention is to provide the operator control stick with an electro simulated variable rate feel system. The simulated feel system provides the operator with proper force feel characteristics while commanding the boom position. During the free-flight mode, the boom commander directs the boom position through a force feel control stick. Stick position, in turn, commands the boom control surfaces until the boom nozzle is in alignment with the receiving aircraft receptacle. Upon alignment, the operator extends the telescoping section of the boom to couple the nozzle and the receptacle.
Another object of this invention is to provide a control mechanism which may be easily and accurately controlled by the operator. The linkage mechanism shifts the center of rotation of the control stick from the mechanical pivot axis to a virtual pivot axis located essentially at the operator's wrist in the pitch axis of control. The control grip rotates about a longitudinal axis located under the operator's forearm to achieve lateral control by slight rotation of the forearm on the armrest.